The present invention relates to ink additives for improving deceleration in ink jet inks containing polymers. More particularly, the present invention relates to ink additives that reduce the deceleration.
Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, or textiles. Essentially, ink-jet printing involves the ejection of fine droplets of ink onto print media in response to electrical signals generated by a microprocessor.
In general, a successful ink set for color ink-jet printing should have the following properties: good crusting resistance, good stability, proper viscosity, proper surface tension, good color-to-color bleed alleviation, rapid dry time, no negative reaction with the vehicle, consumer-safety, good permanence (e.g., smearfastness, lightfastness, waterfastness), and low strike-through. When placed into a thermal ink-jet system, the ink set should also be kogation-resistant and have stable drop ejection performance (e.g. little or no drop velocity degradation over time).
There are two basic means currently available for achieving ink droplet ejection in ink-jet printing: thermally and piezoelectrically. In thermal ink-jet printing, the energy for drop ejection is generated by electrically-heated resistor elements, which heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble, resulting in the expulsion of ink through nozzles associated with the resistor elements. In piezoelectric ink-jet printing, the ink droplets are ejected due to the vibrations of piezoelectric crystals, again, in response to electrical signals generated by the microprocessor. The ejection of ink droplets in a particular order forms alphanumeric characters, area fills, and other patterns on the print medium.
One major drawback of pigmented inks in thermal inkjet printers is the formation of a pigmented film on the resistor surface during prolonged printing. The formation of this film results in a steady and continuous loss of heat transmission to the ink resulting in a phenomena called xe2x80x9cdecelerationxe2x80x9d, or decel, which, in thermal ink-jet technology, refers to a decrease of drop velocity during continuous firing of a nozzle or nozzles. This can lead to drop misdirection, misplacement, or even nozzle turn-off (where velocity equals 0). It is understood that the presence of organic acids serve to prevent the formation of transient insoluble material that can affect heat transfer from the firing resistor to the ink, thereby causing inefficient drive bubble formation, which in turn causes decel.
Decel is often caused by low solubility of the polymer, which is added to improve durability of the ink. One common way to solve decel is to use a inks containing hydrophilic polymers, such as the aqueous inks containing polymers (e.g., acrylate binders) disclosed in U.S. Pat. No. 5,180,425, the entire contents of which are hereby incorporated by reference. Doing so, however, typically leads to a reduction in the waterfastness of the ink.
As previously discussed, ink compositions are required to have certain characteristics. However, few ink compositions are known that possess all the aforementioned properties, since an improvement in one property often results in the degradation of another property.
In accordance with the invention, an ink-jet liquid, an ink-jet liquid set, and the method for using the same are provided, wherein the one of the liquids comprises an aqueous vehicle, and a component capable of alleviating decel in inks containing polymer(s) (acrylate binders), the decel-alleviating component being capable of undergoing rapid thermal decomposition upon heating.
The present formulations are used to formulate ink-jet liquids for use with inks having polymer(s), and more particularly, to provide enhanced drop ejection performance in such ink compositions, such as decel, when the liquid contains a decel-alleviating agent, such as, an aromatic glycol ether, a polar solvent and a long alkyl chain surfactant.